There are many different types of wood chips that can be used in a wood-burning pit, wood-burning grill or even a gas grill. Some of the more popular types of wood chips are apple, oak, mesquite, hickory, cherry, pecan, alder, maple, elm, pear, peach, beech, birch and many more. To use them in a pit, grill or a gas grill unit you will need to use a cast-iron smoker box for (or use aluminum foil heavy-duty) to keep them from burning up. You soak them in water or apple juice for at least one hour prior to use.
This is leisure time, after all, so buy several different types and see what best suits your palette.